The continuing thrust towards digital printing of photographic color papers has created the need for a consumer color paper that can work in both a negative working optical and digital exposure equipment. In order for a color paper to correctly print, utilizing a color negative curve shape of the paper is critical. In a digital environment (direct writing) to a photographic paper, the curve shape to a degree can be electromodulated and thus have a greater degree of freedom than the color negative working system. Ideally, a color paper that could substantially maintain tone scale from conventional optical negative working exposure times to sub microsecond digital direct writing exposure times would be preferred. This would enable a photofinishing area to maintain one paper for both digital and optical exposure thereby reducing the need for expensive inventory.
Typical photographic color print media comprises a multilayer structure having three light sensitive silver halide image recording layers, as well as other non-light sensitive interlayers. The image recording layers typically comprise silver halide and a dye-forming coupler. During photographic processing the silver halide reacts with developer to form oxidized developer (Dox) that undergoes further reaction with coupler to produce image dye, preferably in the same image recording layer in which the Dox is formed. Because Dox can migrate to other layers in the structure, it is possible for it to react with the wrong coupler and form unwanted dye. The term "chemical cross talk" refers to the formation of unwanted dye caused by migration of oxidized developer from one image recording layer to another. One aspect of interimage in photographic paper relates to the propensity of chemical cross talk occurring during development. Papers with high interimage show degraded color reproduction and have a more restricted color gamut (range of accessible colors) relative to a paper having low interimage that produces the same image dyes. To control cross talk image recording layers are surrounded by non-light sensitive interlayers that contain reactive chemicals known in the trade as "scavengers", organic compounds that convert oxidized developer back to developer, or a noncolored by-product before the oxidized developer can migrate to an adjacent color record and form unwanted dye.
Scavengers are typically organic reducing agents, including but not limited to, compounds known in the trade as hydroquinones and their derivatives.
A limitation of organic reducing agents as interlayer scavengers is their reactivity with image dye after photographic processing. Because scavengers are retained in the coating after photographic processing, conditions that promote diffusion of the scavenger into a dye-containing layer may lead to dye destruction due to reaction of the scavenger with the dye to form colorless by-products. Common surface treatments, such as embossing, promote the migration of scavengers into image layers by subjecting prints to localized high pressure (.about.5000 psi) and/or organic solvents.
Another limitation relates to the migration of scavenger into the dye-forming layers prior to photographic processing. In this case, the scavenger may compete for Dox with dye-forming coupler and cause less efficient dye formation, resulting in loss of desired density and/or contrast. In particular, dispersions of magenta dye-forming couplers derived from pyrazoletriazoles are susceptible to scavenger competition. Neutral flat fields that develop to a more green looking neutral at the slit edge of a coating illustrate this problem. The cutting knives may subject the coating to enough local stress to force the scavenger into the magenta dye forming layer, causing this layer to develop to a lower density on the edge of the coating.
Scavengers also interfere with the light stability of the image dyes either by direct reaction with the dye when exposed to light, or by reaction with other components such as UV dyes and chemical stabilizers that are coated with photographic couplers to protect the image dyes from exposure to light. Destruction of the UV dyes or stabilizers enhances the rate of fade of the image dye.
Scavengers also limit the inherent chemical efficiency of a photographic system because Dox is lost to reactions that produce no image dye. Raising the level of silver to compensate for the loss of Dox can lead to increased chemical cross talk and process sensitivity. More efficient conversion of Dox to image dye permits lower silver lay downs and shorter development times for a given density.
These problems have been described in detail in U.S. Pat. No. 5,736,303 which teaches the preferred ratio of gel to organic component in the coating layers to minimize scavenger migration. It would be more preferred, however, to substantially or completely eliminate the scavengers in the interlayers while retaining good color purity.
R. W. G. Hunt, The Reproduction of Color in Photography, Printing and Television, 4th Edition, Copyright 1987, Fountain Press, Chapter 8, Plate 10 describes the structure of conventional color paper and shows the interlayers separating the three dye forming image layers.
U.S. Pat. No. 5,744,287 teaches preferred dye characteristic curves for a conventional paper in a sub-50 microsecond exposure.
Lower contrast toe regions of the paper H&D curves can alleviate contouring. Kokai JP 05/142712-A of Kawai teaches the preferred toe shape of the characteristic dye curve in a scanning exposure employing 10 bit modulation.
U.S. Pat. No. 5,576,159 describes a photographic element having a color enhancing layer in between an emulsion layer and an oxidized developer scavenger layer U.S. Pat. No. 4,040,829 describes a photographic structure where a semi-diffusible coupler layer is coated on top of the topmost emulsion layer.
European Patent Application No. 0 062 202 describes a structure in which the emulsion layers are sandwiched between two coupler containing layers.
Japanese Kokai Patent Application No. Sho 53[1978]-65730 teaches using an additional 0.01-0.3 g/m.sup.2 of yellow coupler in the interlayer between the blue light sensitive layer and the green light sensitive layer.